This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-238772, filed Aug. 25, 1999, the entire contents of which are incorporated herein by reference.
This invention relates to a magnetic resonance imaging apparatus configured to use magnetic resonance (MR) to obtain a magnetic resonance image of a to-be-examined subject, and more particularly to a magnetic resonance imaging apparatus designed to perform a monitor scan for observing the flow of a contrast agent injected into a to-be-examiner subject, and perform an imaging scan for acquiring a photographic image when it is confirmed that the contrast agent has reached a diagnostic region in the subject.
In the field of magnetic resonance imaging apparatuses, several imaging methods suitable for particular diagnosis are proposed. Some MR contrast imaging methods use a function entitled xe2x80x9cVisual Prepxe2x80x9d. In MR contrast imaging methods using the Visual Prep function, a contrast agent is injected into a to-be-examined subject, and a monitor scan is executed. During the monitor scan, a plurality of monitor images are continuously generated and displayed on a monitor. The operator observes the flow of the contrast agent based on monitor images.
Upon confirming the arrival of the contrast agent at the desired diagnostic region, the operator inputs an instruction to execute an imaging scan. By the imaging scan, an MR contrast image to be used for diagnosis can be acquired at an appropriate point in time. A preparatory function that performs the monitor scan may be called a xe2x80x9cVisual Prepxe2x80x9d function.
The conventional technique using a Visual Prep function, however, is disadvantageous in that it cannot follow movement of the to-be-photographed subject (for example, movement of the human body), which occurs during the monitor scan. Specifically, in a conventional Visual Prep function, a mask image (a parent image) of the to-be-examined subject acquired at the initial stage, and a plurality of live images acquired at regular intervals are used. Each time a live image is acquired, the mask image and the live image are subjected to subtraction processing, and the resultant subtraction image is displayed on the monitor. Further, in a conventional Visual Prep function, the live image is updated at regular intervals, while the mask image is not updated but, instead, the initial mask image is used at all times. Therefore, when the to-be-examined subject moves, subtraction processing cannot be executed appropriately, resulting in an inappropriate monitor image.
Once the inappropriate monitor image is displayed, the operator cannot clearly observe the flow of contrast agent. This means that the operator may miss the desired timing for inputting an instruction to execute an imaging scan, and hence may fail to acquire a desired MR contrast image.
The present invention has been developed in light of the above, and aims to provide a magnetic resonance imaging apparatus which can more effectively display a monitor image showing the flow of contrast agent into a to-be-examined subject, thereby enabling the operator to determine appropriate timing for an imaging scan and hence more easily obtain a desired MR image.
According to the present invention there is provided an image display method employed in a magnetic resonance imaging apparatus that executes preparatory imaging, comprising the steps of: collecting a series of magnetic resonance images of a to-be-examined subject, which are to be used for preparatory imaging; determining at least one of the series of magnetic resonance images to be a parent image; creating a difference image between a latest one of the series of magnetic resonance images and the parent image; displaying the difference image on a monitor; updating the parent image in response to a first outside instruction by replacing the parent image with the latest image; displaying, on the monitor, the difference image based on the updated parent image; and collecting a photographic image in response to a second outside instruction.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.